The invention relates to a hydraulic shock absorber as defined herein. A shock absorber of this type is known (German Patent No. 33 12 899).
This known hydraulic shock absorber has a stepping motor, with which a rotary slide is rotated in increments until the rotary slide faces corresponding openings in the piston rod. The stepping motor operates by the reluctance principle. A magnetically conductive sheath has soft magnetic cams that are attracted by electromagnets located in the stator and are thereby rotated into a predetermined position. The drive is based on the different magnetic conductances brought about by the cams. It is therefore impossible to use a smooth-surfaced rotor.
The motion of the cams in a fluid generates considerable fluid friction, resulting in major damping of the system. Because the viscosity of the damper fluid is dependent on temperature, the damping is variable as a function of temperature and must be taken into account when the system is regulated.
Without considerable additional expense for electronics (half-step method), there is a relatively high lower limit to the step size of the stepping motor. Fine gradations are therefore impossible. The step size of a given stepping motor is invariable and hence cannot be adapted during operation to prevailing requirements.
The stator winding of the drive comprises a plurality of coils, through which current flows in alternation. The torque is therefore always produced by only a single coil at a time, which means that a large proportion of the available winding space at a given moment goes unused.
To effect a reset for safety reasons in the case of defective triggering, a restoring spring is provided, but its use also has disadvantages.
Since the known shock absorber has a piston with mechanical compression springs for a basic damping valve, only a bypass throttle cross section is changed by the aforementioned rotary slide valve.
By disposing the throttle cross section in the hollow piston rod, finally, the total cross section is limited by the rod diameter and cannot be optimally adapted to a required total flow.